Expectations for a display apparatus using a plasma display panel (hereinafter referred to as a “PDP”), which displays an image of high definition TV as a large screen, has been rising.
The PDP is basically formed of a front plate and a rear plate. The front plate is formed of a glass plate, display electrodes, a dielectric layer and a protective layer made of MgO. The display electrode, which is formed of a striped transparent electrode and a striped bus electrode, is disposed on one surface of the glass substrate. The dielectric layer covers the display electrodes and works as a capacitor. The protective layer covers the dielectric layer.
A glass produced by a float process (hereinafter referred to as a “float glass”) is used as the glass substrate, because a flat and large glass is easy to be produced by the float process. The transparent electrode is formed on the glass substrate by a thin film process, and paste including silver material is applied on the transparent electrode in a certain pattern for securing electrical conductivity. Then the paste is fired so as to form the bus electrode. In addition, paste for a light shielding layer is applied in a certain pattern and fired for improving contrast. Dielectric layer paste is applied in a manner to cover these whole electrodes and fired. Finally, the protective layer made of MgO is formed by a well-known thin-film-forming method.
On the other hand, the rear plate is formed of a glass substrate, address electrodes, a dielectric layer, barrier ribs and a phosphor layer. The address electrodes are disposed on a surface of the glass substrate in a striped pattern. The dielectric layer covers the address electrodes, and the barrier ribs are disposed thereon. The phosphor layer is formed between the barrier ribs, and emits red, green or blue light.
The front plate and the rear plate are faced and stuck each other on their electrode surfaces. Discharge gas such as Ne-Xe is sealed into discharge space formed with the barrier ribs at pressure of 400 Torr—600 Torr. The discharge gas is discharged by selectively applying a video signal to the display electrode, whereby an ultraviolet light is generated and excites the phosphor layer. As a result, red, green and blue light are emitted, thereby displaying a color image.
Japanese Patent Unexamined Publication No. H10-255669 or H11-246238 discloses that when a float glass is used as a front plate and an electrode including silver material is formed thereon, a colored layer is formed on a surface of the float glass, so that the float glass is tinged with yellow.
A phenomenon in which the float glass colors by the silver electrode is considered as follows: Silver colloid is generated by an oxidation-reduction reaction of silver ion (Ag+) and reducing tin (Sn) which exist on the float glass, whereby light absorption is caused at approximately from 350 nm to 450 nm of wavelength.
In other words, the float glass is subjected to a hydrogen atmosphere in its producing process, so that a reduced layer having a thickness of several microns is generated on the surface of the float glass, and tin ions (Sn++) resulted from melted tin (Sn) are existed therein. Silver ions (Ag+) leave from the bus electrode by heat generated at a process in which the bus electrode made of silver (Ag) is formed on the glass substrate via the transparent electrode. These silver ions (Ag+) diffuse on the transparent electrode and reach the surface of the glass substrate, and ion-exchange occurs with ions of alkali metal included in the glass substrate, so that the silver ions (Al+) penetrate into the glass substrate. The penetrated silver ions (Ag+) are reduced by tin ions (Sn++) existed in the reduced layer, and form metal silver colloid (Ag). The glass substrate is tinged with yellow by the silver colloid (Ag). The float process is suitable to produce a glass substrate used at a large-sized display device such as the PDP, however, the glass substrate is produced on melted tin (Sn), so that tin (Sn) is inevitably stuck into the glass substrate.
Yellow coloration of the glass substrate mentioned above sometimes causes a serious damage for the large-sized display device such as the PDP. That is because luminance of a blue color decreases by coloring of the glass substrate, and chromaticity changes. Particularly, in displaying a white color, a color temperature or the like is reduced, so that picture quality deteriorates. In addition, the whole display area of the PDP looks yellowish, so that a commercial value falls. Japanese Patent Unexamined Publication No. H10-255669 discloses the following technology: Coloring, which is caused by using the electrode containing silver, of the glass substrate is restricted by abrading a surfaced of an electrode of the glass substrate and removing the reduced layer formed thereon. Using this technology, a glass substrate, which is not colored much, can be produced. However, a process of removing the surface of the electrode is needed for manufacturing processes of the glass substrate of the PDP, so that productivity is a problem to be solved.
The present invention is directed to provide a method of manufacturing a plasma display panel which can restrict the coloring (yellow coloration) of the glass substrate caused by silver ions (Ag+), when the electrode is formed on the float glass by using material containing silver (Ag).